Method of protecting carbonaceous material from oxidation at high temperature

ABSTRACT

Oxidation resistance is imparted to all-carbon bodies by applying a phosphoric acid solution of manganese pyrophosphate thereto and heating the coated body to a temperature of 500* C or greater for approximately 5-10 minutes.

V JQI LJQOOL United SttltCS Patent 11 1 DeBrunner etal.

1 51 Jan. 30, 1973 i541 METHOD OF PROTECTING CARBONACEOUS MATERIAL FROM OXIDATION AT HIGH TEMPERATURE [76] Inventors: Ralph E. DeBrunner, 4717 Connel Dr., Raleigh; Patricia C. Clements, 1000 N. Duke St., Durham, both of NC.

[22] Filed: Mareh 5, 1971 [21] App]. No.: 121,451

[52] U.S. Cl. ..117/l69 R,-l 17/228, l48/6.l5 R

[51] Int. Cl. ..B44d H20 [58] Field of Search ..117/l23 A, 169 R, 228, DIG.

[56] References Cited UNlTED STATES PATENTS 2,715,080 8/l955 Cashell ..1 17/223 2,685,541 8/1954 Woodburn et al.....

2,685 54O 8/]954 Woodburn et al ..l 17/228 X Primary Examiner-Ralph S. Kendall Assistant Examiner-Caleb Weston v Att0rneyVance A. Smith, J. Bowen Ross and Neal E. Willis ABSTRACT Oxidation resistance is imparted to all-carbon bodies by applying a phosphoric acid solution of manganese pyrophosphate thereto and heating the coated body to a temperature of 500 C or greater for approximately 5-l0 minutes.

2 Claims, 2 Drawing Figures TIME (HOURS) PATENTED JAN 3 0 I973 TEST TEMPERATURE 680 c WITH $0 :35; EHEE TIME HOURS) FIG. I.

TEST TEMPERATURE 800 C TIME (HOURS) FIG, 2.

METHOD OF PROTECTING CARBONACEOUS MATERIAL FROM OXIDATION AT HIGH I TEMPERATURE "CROSS-REFERENCE TO RELATED INVENTIONS This application is related to copending application Ser. No. 866,116 filed Oct. 8, 1969, now U.S. Pat. No. 3,639,197, of Raymond G. Spain.

.FlELDOFTHElNVENTlON 4 The present invention relates to improving the oxidation resistance of all-carbon bodies through application of an inorganic solution to the oxidatively exposed surfaces of all-carbon bodies.

BACKGROUND OF THE INVENTION carbonaceous items have found a wide range of industrial and aerospace applications due to combinations of generally desirable properties which include electrical conductivity, thermal conductivity, thermal heat capacity, resistance to thermal'shock, high thermal stability, friction and wear characteristics, and chemical resistance to environments which are not strongly oxidative in nature.

Applications of such products include bearings, seals, electrodes, heating elements, electrical contacts of a wide variety and as materials for containing and conducting corrosive materials, such as in heat exchangers.

materials. The strength of essentially all-carbon materilug areas due to a belt of carbon fibers which reinforce the disc.

The problem of oxidative susceptibility, however, is

severe for all-carbon composites when employed at elevated temperatures such as the levels present when aircraft brake discs are operated. While it is well known that the oxidative resistance of homogeneous and composite carbonaceous materials can be significantly enhanced by the addition or in situ formation of selected borides, nitrides, and carbides, these added or formed modifiers detract from theperformance of such items as otherwise all-carbon composite brake discs due to undesirably altered thermal, frictional, or wear characteristics.

It is therefore the primary object of this inventionto provide a carbonaceous body, including an all-carbon composite body which will resist oxidation at high temperatures by modifying theformed carbonaceous body by a coating of the exterior of the body. I

SUMMARY An all-carbon body is provided with oxidation resistance to temperatures of 760 C or above by applying a phosphoric acid solution of manganese pyrophosphate thereto and heating the coated body to a temperature of 500 C or greater for approximately 5-10 minutes. Resulting measurements show little weight loss due to oxidation after prolonged exposure to air at temperatures of 760 C and higher.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the invention desired to be protected are pointed out in particularity in the appended claims. The invention itself may be best understood by reference to the following description and accompanying drawings in which:

FIG. 1 is a comparison graph of the weight loss of a carbon body with the oxide inhibitor of the present invention to one without the inhibito h ertexposed to EXAMPLEI An all-carbon composite test specimen identical to the compositions described in the referenced application was soaked for approximately 10 minutes in a phosphoric acid solution of manganese pyrophosphate of the following weight ratiosi 28% H O/50% H PO /2 2% MnP O-, 7H O. The coated specimen then was heated in air for approximately 5-10 minutes at a temperature of about 760 C.

Coated and uncoated specimens were next subjected to oxidation in air at various temperatures for about 60 minutes. The oxidation resistance index, i.e., wt. loss of coated specimen)/(% wt. loss of uncoated specimen) X 100, was then determined and recorded in Table l. g

TABLEI Oxidation Temperature ORI 760C (l400F) 0 870C (l600F) 25 980C (l800F) 65 EXAMPLE 2 It is often desirable to protect only particular regions ofan all-carbon composite. Because the technique of Example I employs air during the heat treatment, uncoated regions would undergo oxidation. In this example, a nitrogen atmosphere was used during heat treatment since nitrogen is unreactive either with the solution or all-carbon composite specimen. The solution employed was identical to that used in Example 1. The specimen was heated at a temperature of about 500 C for approximately 5-10 minutes. Representative data is found in Table 2 below. The data again indicated a significant increase in oxidation resistance as compared to uncoated all-carbon specimens.

TABLE 2 Oxidation Temperature ORl 760C 870C 25 I 980C 60 EXAMPLE 3 limited to the preferred percentages in deference to the best technique of making the oxidation resistant article. It should be noted, however, that other percentages may also be used as limited by the following ranges: 25-30% H O/45-55% H PO /20-25% MnP O 7H O.

What we claim is:

t 1. An all-carbon oxidation resistant body having a coating formed by applying a phosphoric acid solution of manganese pyrophosphate in the weight ratios of 25-30% H O/45-55% H PO /20-25% M11 50, 7H O and heating the coated body to a temperature of at least 500 C for approximately 5-l0 minutes.

2. The oxidation resistant body of claim 1 wherein the phosphoric acid solution of manganese pyrophosphate is in the weight ratio of 28% H O/50% H PO /22% Mn P O 

1. An all-carbon oxidation resistant body having a coating formed by applying a phosphoric acid solution of manganese pyrophosphate in the weight ratios of 25-30% H2O/45-55% H3PO4/20-25% Mn2P2O7 . 7H2O and heating the coated body to a temperature of at least 500* C for approximately 5-10 minutes. 